Can We Use δ13C of CO2 to Understand the Links Between the Water and Carbon Cycles and Climate?
C. Alden1, J.B. Miller2, J.W.C. White1, V. Yadav3, A. Michalak3, A.E. Andrews4 and L. Huang5
1Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80309; 719-930-5281, E-mail: firstname.lastname@example.org
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309
3Carnegie Institution for Science, Department of Global Ecology, Stanford, CA 94305
4NOAA Earth System Research Laboratory, Boulder, CO 80305
5Environment Canada, Toronto, Ontario M3H 5T4, Canada
The fate of the Earth’s climate is intricately linked to that of the global carbon cycle. Much uncertainty remains about those links and the potential responses of both systems to recent and ongoing human perturbations. Different attributes of atmospheric CO2 (e.g. spatial gradients and relative abundances of its isotopologues) provide evidence of the mechanisms that link climate and the carbon cycle. The stable carbon isotope, 13C, is a useful tracer for understanding terrestrial biosphere to atmosphere CO2 exchange (as well as for partitioning land and ocean CO2 fluxes) because photosynthesis discriminates strongly against heavy CO2 (and ocean exchange does not). The degree to which photosynthesis fractionates against 13C depends upon: 1) plant functional type distributions, because C3 and C4 plants have very different discrimination, and 2) weather and climate conditions, because stomatal conductance is closely related to C3 plant isotopic discrimination.
To investigate these processes, we use a two-step Bayesian inversion model to optimize 1x1 degree and 3-hourly (interpreted at the monthly scale) fields of δ13C of the biosphere over North America for the year 2010.
We also examine correlations between atmosphere δ18O of CO2 and climate records. This tracer offers complementary insights into biosphere atmosphere CO2 exchange because of the close relationships between δ18O and relative humidity and precipitation.
Figure 1. July 2010 SiB2 δ13C of the biosphere.